A high school romance gone bad is rocking Pace University — with the bitter former lovebirds turning the school into their own personal war zone, according to a new Manhattan lawsuit.

Freshman Ari Grossman filed a lawsuit in Manhattan federal court saying his ex-girlfriend and current classmate Kalya Torrey started their vicious feud by lying that he raped her in order prevent him from attending Pace — his dream college.

Grossman said he and Torrey ended their Malibu, Calif., romance when they were 15 years old — but that they parted amicably. He had no idea there was bad blood until after he had been admitted to Pace’s acting program, which prompted Torrey’s parents to call his parents and demand he drop out, the lawsuit said.

After Grossman refused to drop out, Torrey asked the District Attorney’s Office to bring charges, although none was filed, the lawsuit said. Torrey then sought a temporary restraining order against Grossman, but the judge ordered the Malibu residents to settle the case and they agreed to just stay away from each other, the lawsuit claimed.

Once at school, the situation escalated — with each side accusing the other of stalking and harassment.

Torrey filed so many complaints against Grossman in the first few weeks of school — seven between Sept. 4 and Sept. 11 — that the dean had to intervene and tell them to just cool it, Grossman’s suit says.

The final straw for Grossman came when his ex accused him of stalking her in the food hall in November — and he ended up getting tossed in a cell for 12 hours with his legs and hands in shackles.

He was released from custody after being charged with criminal contempt.

The NYPD has since dropped the charges after video surveillance from that day failed to prove stalking, the lawsuit said.

Still, Grossman is suing the school and Torrey for having him improperly arrested via campus security. He also expects to add the NYPD to the list of defendants as soon as the proper paperwork is filed, his lawyer Julie Goldberg told The Post.

“It’s just been a horrible college experience for him,” Goldberg said. “We feel at this point he is not being protected.”

Torrey’s father Michael, who designs and builds custom homes, declined to comment on the lawsuit or what he called “a sad situation.”

“Obviously we don’t agree with anything” in the lawsuit, he said. “But we think it is inappropriate to comment.

“This is playing with these kids’ lives and it’s a sad situation,” he added.

Pace also declined to comment, with spokesman Scott Trent saying that the school has not yet been served with the complaint.